Oscillation generator



- May 10, 1932.

' A. w. HULL OSCILLATION GENERATOR Original Filed Feb. 26. 1926 H/G-l-l NATURAL FJ'E l/EIVOY Inventor Albert W. l' lu|l,-

His Attofn ey.

Patented May 10, 1932.

UNITED STATES PATENT orrlcs mm! W. HULL, OF SCHENECTADY, NEW YORK, .ASSIl'iIN'OB- TO 4! ILEGTBI COMPANY, .A-COBIPORA'I'ION' NEW YORK oscma'rxon ammnA'ron Application filed February 28, 1926, Serial at. 90,958. Benewed July 81, 1981.

5 oscillation of the piezo electric. element forming a part of such a generator-may be readily started and thereafter maintained or reproduced at a predetermined fre uency.

It is well known that an oscillating piezo 30 electric element, such as a slab or disk of quartz, will continue to oscillate when subjected to voltage at a frequency dependent on its mechanical dimensions. When a piezo electric element is utilized to predetermine' the oscillation frequency of a circuit comprising an electron discharge device, oscillation of the piezo electric element is apparently started by the relatively small variations in the electron emission of the cathode of the device. These slight varitions change the eleciezo electric trostatic stress applied to the element and produce a train 0 compression and expansion waves throughout the element at a frequency which is dependent on the as mechanical dimensions of the element. The

comparatively feeble train of waves thus produced, by virtue of their mechanical effect" upon the element, cause electromotive forces of a predetermined frequency to be applied 80 to the grid of the electron discharge device, and this electromotive force functions to amplify the originally feeble electrostatic stresses impressed on the piezo electric element to such an extent that they determine the oscillation frequency of the generator output circuit.

In utilizing a piezo electric element to predetermine the oscillation frequencyof a circuit, difliculty is encountered in arranging the circuits so that the generator always operates at a frequency which is reproducible and is unaffected by feed back through the generatoroutput circuit. This difliculty is a largely due to the fact that a piezo electric element may oscillate at several difierent frequencies.

In accordance with my invention, operation of the generator at a frequenc readily reproduced is ensured by the use 0 an elec-' tron discharge device which has a high mutual conductance and is connected to a circuit turned to a frequency higher than that at which it is desired to operate the generator, and feed back from the output circuit is preinterposed between its control grid and its anode.

My invention will be better understood from the following description when considered in connection with the accompanying drawing and its scope will be pointed'out in the a pended claims.

Re erring to the drawing, the single figure an output circuit 8 which is coupled to the amplifier 4. through a transformer ,9. The electron discharge device 3 comprises a cathode 10, space charge and control grids 11 and 12, and an anode 13. The amplifier 4 is provided with a cathode 14, control and screen grids 15 and 16 and an anode 17. Heating current is supplied to the cathodes 10 and 14 from a source 18.

The cathode 10 is connected to the control grid 12 through the piezo electric element 2 which is shunted by a id leak resistor 19, to the space charge grid 11 through a low voltage tap 20 of the anode current source 21, and to the anode 13 through the source 21 and a reactor 22 whichis preferably of an impedance just high enoughto ensure operation of 55 vented by a thermionicamplifying element of the type having an auxiliary screen grid the oscillation generator. The output current of the amplifier 4 is supplied from a source 23 which is connected between the cathode 14 and the anode 17 through a circuit which comprises a condenser 24 and the primary wlndm of the transformer 9 and which is preferably tuned to the frequency of the piezo electric element 2. It Will be observed that the screen or shield grid 16 is connected to a low voltage tap 25 of the source 23, and that the control grid 15 is connected to the cathode 14 through a resistor 27 and grid bias means shown as a battery 26.

Certain conditions are essential for, stable operation of the generator 1. It is desirable that the natural period ofthe circuit comprising reactance device 22 be made of short duration compared with the mechanical period of the crystal in order that oscillation of the iezo electric element 2 be established at a requency which is exactly'reproduced each time the generator is put into operation. If the impedance of this circuit is decreased beyond a certain value, however,.the device 3 will not oscillate and the generator 1 will fail to operate. Operation of the generator at a definitely reproducible frequency is ensured whenthe anode circuit of the device 3 is made be so small, due to the low impedance ofthe plate circuit load 22 at the desired frequency,

that the generator will not function. This difficulty I have overcome by designing the reactor 22 to have maximum inductance and minimum distributed capacity, and by using for the device 3 a tube with high mutual conductance, preferably of the space-charge grid type shown. In this way stable continued operation of the generator may be assured.

With a proper choice of circuit constants and with the temperature of the piezo electric element maintained constant, the frequency of the generator remains constant to less than one part in a million. This frequency is thus practically independent of all ordinary fluctuations of supply voltage and such changes of circuit constants as are incident to temperature variation or chance mechanical movement.

, When current from a generator of the type described is supplied to an output circuit, the output circuit will generally react on the generator to alter its frequency. This reaction is smallest when the generator is loosely coupled to the grid of a thermionic amplifier interposed between the generator and output circuit. ,Even in this case, however, tuning of y the amplifier anode circuit by the condenser 24 will in general change the frequency of the generator by ten to one hundred parts in a million due to the capacity reaction between enerator. Under these conditions, the

the plate and control grid of the amplifier. By the use of the screen grid between control grid and anode, all danger of feed back is avoided and the frequency of the generator is rendered independent of change in the constants of the output circuit.

The embodiments of the invention illustrated and described herein have been selected for the purpose of clearly setting forth the principles lnvolved. It will be apparent, however, that the invention is susceptible of being modified to meet the different conditions encountered in its use and I therefore aim to cover by the appended claims all modifications within the true spirit and scope of connected between said cathode and said grid for predetermining the frequency of the por tential of said id and a circuit interconnecting said cat ode and anode and having such constants that the circuit is tuned to a frequency at least twice that predetermined by said piezo electric element.

2. The combination of an electron dischar e device provided with a grid for controlling the transmission of current between its cathode and anode and with a space charge grid interposed between said cathode and said control grid, a piezo electric element connected between said cathode and said control grid for predetermining the frequency of the otential of said grid, a circuit interconnecting said cathode and anode and tuned to a frequency higher than that predetermined by said piezo electric element, means for applying a, potential between said cathode and anode, and means for applying tosaid space charge'grid a'potential intermediate that of said cathode and anode.

r 3. The combination of 'an electron discharge device'comprising a grid for controltween said cathode and anode, and tuned to a frequency higher than that predetermined by said piezo electric element, and a thermionic amplifier provided with a cathode, an anode, a control grid and a screen grid interposed between said control grid and said anode, the control grid circuit of said amplifier being coupled to said tuned circuit.

4. The combination of an electron dis-,

charge device comprising a grid for controlling the transmission of current between its cathode and anode, a piezo electric element connected between said cathode and said grid between said control grid and said anode, the controlgrid circuit of said amplifier bein coupled 'to said tuned circuit, and a tune out ut circuit connected between thecathode an anode of said amplifier.

5. The combination of an electron dis chargedevice comprisin a grid for controlthe transmission o current between its. 'cat ode and anode, a single piezo electric element connected between said cathode and said grid for predetermining the frequency of the potential of said grid, a circuit connected between said cathode and anode, and a reactance device connected in said circuit having such constants that said circuit is tuned to a freuency higher than and widely different from i t at predetermined .by said piezo electric device, said reactance device being designed to have a relativel high inductance and a'relatively low distributed capacity.

6. The combination of an electron discharge device comprising a grid for controlling the transmission of currrent between its cathode and anode, a piezo electric element connected between said cathode and said grid for predeter'mining the frequency of the tential of said grid, a circuit connected hetween said cathode and anode, and a relatively high impedance and low distributed capacity tuning device included in said circuit having such constants that said circuit is tuned to a frequency higher thanthat determined by said piezo electric device.

7. In combination, an electron discharge device, having a grid, an anode and a cathode, a piezo electric element connected between the grid and cathode of said discharge device, a source of anode-potential connected between said anode and said cathode throu h v an inductance coil, a second electron discharge device havin an anode, a cathode, and a grid, the gri of said second device being connected to the anode of said first device through a condenser and the cathodes of said devices being connected together, biase grid and cathodeof said. second device, and a circuit tuned to the frequency of the crystal con nected. between the anode and cathode of said second device, said inductance coil comprising the sole tuning element in circuit between said discharge devices, and having a natural frequency which is widely different from the frequency of the crystal;

8. The combination of an electron discharge device having an anode, a cathode,

and a plurality of additional electrodes interposed between said anode and cathode, a

i da through said other device to said 10 cuit, an additional electrode inter osed bc-' connection between said anode and cathode inc'ludin' a source of electromotive force and .an impe ance, a piezoelectric element connected to-one of said additional electrodes to impress thereon an electromotive force having a, frequency determined by the natural frequency of said piezo-electric element, said mgedance having a natural frequency widely erent from the natural frequency of said piezo electric element, and the other of said additional electrodes being arranged between said one additional electrode and said cathoile anld cgmfiected to said soluroe.

.9. n a, i requenc signa ing stem 'an/electron dichar e oscillator including all output'circuit, an e ectron discharge ampli-" fier having an anode, a cathode and a control electrode, a load circuit for said amplifier, means for supplying high frequency oscillations from said output circuit to the control electrode of said amplifier whereby they are amv lified and supplied to said load circuit, an means for preventing impedance variations in said load circuit from affecting the frequency of oscillations produced by said electron dischar e oscillator, said means comprising an ad itional screening electrode interposed between said anode and control electrode and means. for maintaining said screeningelectrode at a highpositive potential with res ect to the cathode; 10. In com ination, a plurality of electro discharge devices, each of said devices having an anode, a cathode and-a grid, circuit connections between the anode and cathode and between the grid and cathode of one .of said discharge'devioes, said circuit connections being arranged to cause said device to roduce oscillations, a load circuit connected tween the anode and cathode of the other discharge device, a connection between the grid of said other device and said circuit connections whereby oscillations are sup lied tween saidfgrid and cathode of sai one discharge device, means to maintain said additional electrode at hlgh positive tential and 'means included in said other 'scharge device to prevent variations in said load circuit from affecting the frequency produced by said oscillation generator.

11. In combination, a plurality of electron discharge devices, each of said devices having an anode, a cathode and-a grid, 'a piezoelectric element connected to the grid of one of said devices to supply thereto an electromotive force having the natural frequency of said piezo-electric element, a load circuit connected between the anode and cathode of said other discharge device, a connection between the anode of said one discharge device and the grid of said other discharge device whereby oscillations are excited in said load circuit in response to oscillations of said piezo-electric element, an additional screening electrode interposed between the'anode and grid of said other discharge device thereby to pre vent impedance varlations in said load circuit from reacting upon said piezo electric element, and means to maintain said additional screening electrode at hi h positive potential with respect to said cat ode.

In witness whereof, I have hereunto set my hand this 25th day of February, 1926.

' ALBERT W. HULL. 

